Problem: Solve for $r$ : $28 = -28 + r$
Answer: Add $28$ to both sides: $ \begin{eqnarray} \\ \hphantom{28 {+ 28}} &\hphantom{=}& \hphantom{r} \\ 28 &=& -28 + r \\ \\ {+28} && {+28} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ 28 {+ 28} &=& r \\ \end{eqnarray} $ Simplify. $ r = 56$